From my observation the Magnus drop ball will often drop more than the SSW drop. But there are a couple of good reasons to develop the SSW drop. First the break on a Magnus drop is smoother, combining the parabolic arc due to gravity added to the Magnus effect which produces an increasing impact as the ball travels to the target. The break on the SSW drop starts later as there is no force other than gravity at the start. As the low pressure on the bottom of the ball is created the break starts happening and can be sharper than Magnus. Also the spin is unfamiliar to most batters so it is more deceptive.
Many of my students when first learning the SSW rise will pull their fingers up along the side of the ball at release. This generally produces some topspin with the angle of rotation such that the SSW tracking dot will be above the center and to the right (for a rhp). Getting the tracking dot to be 30 degrees above center will allow the long seam to hug the bottom horizon of the ball so that it can produce a pocket of low air pressure on the bottom. The ball will fall into that pressure void. There is also a small amount of Magnus force due to the laces coming over the top of the ball so some degree.
To teach this pitch use a ball marked for a 2 seam fastball with an SSW tracking dot. Grip the ball like a 2 seam fastball with the middle finger on top of the stripe. You can grip it anywhere that feels comfortable for example the finger tips on a seam or two fingers running along the seam or anything that will produce a solid stripe if thrown like a fastball.
The fingers will slide under the ball just like a SSW rise ball. But instead of finishing by coming off the bottom lets the fingers lift the ball just before release. The SSW tracking dot will be located about 30 degrees above the center of the ball and somewhat to the right. This will produce spin just like the SSW rise ball except upside down.
